DESCRIPTION (provided by investigator): This is an application for a 5-year study of decision-making in normal adolescents and substance abusing adolescents whose primary diagnosis is not alcohol. Non-substance abusing adolescents will be public high school students in grades 10, 11 and 12. Substance abusing adolescents, of the same age, will be clients at an adolescent substance abuse treatment center. At initial contact each participant will be given a battery of neurocognitive tasks that measure functions of the prefrontal cortex. These will include two versions of the Iowa Card Task, Wisconsin Card Sorting Task, Stroop task, Object Reversal task, and surveys of sensation-seeking, impulsivity and excitement seeking. Each participant will also be given a clinical assessment and outcomes interview (Comprehensive Adolescent Survey Inventory or CASI). The CASI assesses seven areas of life functioning including substance use, academic problems, legal status, employment history, and sexual behaviors. The CASI will be given at 6-month intervals during a two-year follow up period. One goal of this project is to characterize the neurocognitive functions of adolescent substance abusers and non-abusers. Another goal is to determine if substance abusers' performance on any component of the test battery is predictive of completion of treatment, post-treatment relapse, or other poor-decision making in real life. A third goal is to determine, among non-substance abusers, if performance on any component of the test battery is predictive for those who may become substance abusers and engage in poor decision-making in real life. Characterization of the neurocognitive profiles of adolescent substance abusers or of individuals who are at risk for future substance abuse is a necessary step toward the development of intervention and prevention protocols.